New Correlation for the Prediction of Bursting of a Laminar Separation Bubble

Laminar separation bubble bursting is a deleterious phenomenon resulting in a loss of lift and an increase of drag at relatively low Reynolds numbers. There are some criteria in vogue in the literature to characterize the onset of the bursting phenomenon. A relatively simple one-parameter criterion that was proposed, based on the work done in the authors' laboratory in the past, has been found to bequite successful in characterizing bursting and is well cited in the literature, includingin unsteady flow contexts. This criterion is revisited, and it is reassessed in the light of recent laminar separation bubble measurements over an Eppler 387 airfoil. Building on these foundations, the pursuit of a more robust bursting criterion that could also be predictive in nature led to a new simple criterion. According to this, bursting is signaled by the ratio of the freestream velocity at reattachment to that at separation reaching a critical value of 0.86. New engineering correlations are also proposed for the length and height of laminar separation bubbles that, along with the new bursting criterion, should be extremely useful in the design of low-Reynolds-number aerodynamic configurations.